You can take this as a completely unsolicited product review. I haven't been given any freebies or inducements. I do have a couple of ulterior motives, but those will become clear as you read on.
I'm in love with the PowerGenix batteries. I've been trying to use rechargeable batteries exclusively for years. I've been failing at exclusive, but doing an OK job of reducing my disposables usage. It's become more of an issue since I got a new job and my new place of work doesn't have convenient battery recycling containers. I know that most modern disposables don't have mercury and can, in theory, just go in the trash, but it's still wasteful so send those metals and other refined materials to a landfill when they can be reused. So instead I keep an ever-growing pile of dead batteries until I feel obliged to make a trip to radio shack. Then I feel guilty about dumping a grocery bag of dead batteries on them and buy something I don't really need.
There are a couple challenges to going all-rechargable. The first one (for me) is organization. If you're going on a trip, you need to remember to bring extra charged batteries and/or a charger. I've become pretty good about just keeping an extra little charger with batteries already in it in my bag so it's ready to go, but I still get caught out sometimes. It's not that often, though, and when you're making that pilgrimage to The Exploratorium, you just have to make allowances.
For me the real challenge is making sure there are extra charged cells laying around when I need them. You can never predict when and how many batteries you're suddenly going to need. I finally got around to setting up a well organized (for me) charging station.
As you can see, I have a bin to chuck the discharged cells and a bin for the charged ones. It's located where I walk right by it as I enter the office and it reminds me to check if there's anything in the "charge-me" bin. I pop them into the little 4-cell charger and plug them into the outlet that's right below it. On a later pass I might notice that they're done charging and put them in the "charged" bin. I could make it a regularly scheduled Omnifocus task, because I happen to notice just often enough to keep ahead.
But there's a problem. At least there used to be. When I was using NiMH battries, there wasn't much point in trying to get ahead because the self-discharge rate meant that half the time the batteries were at least half dead when I tried to used them. To make matters worse, the nominal charged voltage if NiMH is 1.2V, which is barely enough to run a lot of electronics that are expecting 1.5. It doesn't take a lot of drop off of fully charged to get that "replace battery" symbol that we all dread. As far as I'm concerned NiMH are a bust. I've never managed to get NiMH to power TV remotes, for instance.
Enter NiZn battery chemistry. These cells are 1.6V at full charge. You might worry that the slightly high voltage could cause problems, but I've yet to find a device where that's the case. Even better, the self-discharge rate is low enough that I can keep a bin full of charged ones for when I need them. These are rechargeables that actually work. Go buy them NOW!
So what's my super-secret agenda? I'll tell you. These aren't a mainstream chemistry. I want them to keep making them. That's it. Oh yeah, and I'd like it to be successful enough that they start making them in other sizes. AAA have recently become available, but I still have a few C and D cell applications, and burning through disposables in those sizes can get expensive.